Benzene, toluene, and xylenes (BTX) are common building blocks of modern petrochemical industries. The present source of these compounds primarily is the refining of petroleum, but alternative sources of aromatics that are independent of refining are desirable. Conversion of various feeds to aromatic compounds becomes an industrially valuable option. Some conventional methods can include conversion of methanol and/or olefins to aromatics in the presence of a molecular sieve, such as ZSM-5. Reactions for conversion of methanol and/or olefins to aromatics can be useful, for example, for creation of aromatics as individual products, or for formation of aromatic and olefin mixtures for use as naphtha boiling range or distillate boiling range fuels.
Methanol can be converted to gasoline employing the MTG (methanol to gasoline) process. The MTG process is disclosed, including, for example, U.S. Pat. Nos. 3,894,103; 3,894,104; 3,894,107; 4,035,430 and 4,058,576. U.S. Pat. No. 3,894,102 discloses the conversion of synthesis gas to gasoline. MTG processes provide a simple means of converting syngas to high-quality gasoline. The ZSM-5 catalyst used is highly selective to gasoline under methanol conversion conditions, and is not known to produce distillate range fuels, because the C10+ olefin precursors of the desired distillate are rapidly converted via hydrogen transfer to heavy polymethylaromatics and C4 to C8 isoparaffins under methanol conversion conditions.
These light aromatics are also produced in a related process for converting methanol to olefins (MTO). U.S. Pat. Nos. 4,049,573 and 4,088,706 disclose conversion of methanol to a hydrocarbon mixture rich in C2-C3 olefins and mononuclear aromatics, particularly para-xylene, by contacting the methanol at a temperature of 250-700° C. and a pressure of 0.2 to 30 atmospheres with a crystalline aluminosilicate zeolite catalyst which has a Constraint Index of 1-12 and which has been modified by the addition of an oxide of boron or magnesium either alone or in combination or in further combination with oxide of phosphorus. The above-identified disclosures are incorporated herein by reference.
More recently, Chinese publications CN 101602648, CN 101602643, CN 101607864, and CN 101780417 describe use of selectivated catalysts for conversion of methanol to para-xylene. According to these publications, zeolite catalysts are treated with silicate compounds, such as tetraethylorthosilicate, to provide improved selectivity for formation of olefins and para-xylene from methanol feeds. However, silicon treatment introduces several undesired effects, e.g. it reduces the per pass aromatic yield and promotes coke deposition that limits the catalyst cycle length. Especially for metal promoted zeolites, silicon treatment can promote metal migration and sintering that result to shorter catalyst lifetime.
In terms of the sources of methanol, there are various ways to produce the product through chemical reactions. For example, synthesis gas (CO+H2) is readily obtained from fossil fuels and can be further converted to lower aliphatic oxygenates, especially methanol and/or dimethyl ether. U.S. Pat. No. 4,237,063 discloses the conversion of synthesis gas to oxygenated hydrocarbons using metal cyanide complexes. U.S. Pat. No. 4,011,275 discloses the conversion of synthesis gas to methanol and dimethyl ether by passing the mixture over a zinc-chromium acid or copper-zinc-alumina acid catalyst. U.S. Pat. No. 4,076,761 discloses a process for making hydrocarbons from synthesis gas wherein an intermediate product formed is a mixture of methanol and dimethyl ether.
Some processes relating to converting syngas to ethanol and C2+ oxygenates are disclosed. EP 010,295A describes a process for preparing ethanol from synthesis gas, in which the reaction is carried out over a supported rhodium catalyst comprising, as co-catalyst, one or more of the elements zirconium, hafnium, lanthanum, platinum, chromium and mercury.
U.S. Pat. Nos. 6,346,555 and 6,500,781 disclose a catalyst and a process for preparing C2− oxygenates by reaction of CO and H2 over a rhodium-containing supported catalyst, in which the catalyst consists essentially of rhodium, zirconium, iridium, at least one metal selected from amongst copper, cobalt, nickel, manganese, iron, ruthenium and molybdenum, and at least one alkali metal or alkaline earth metal selected from amongst lithium, sodium, potassium, rubidium, magnesium and calcium, on an inert support.
However, there is an ongoing need to provide improved catalyst systems and processes for producing aromatics from various feeds, such as alcohols. An object of this disclosure is to increase the conversion of syngas to aromatics, and obtain a final aromatic product rich in benzene, toluene, and xylenes (e.g. greater than 50% aromatics on a hydrocarbon basis).